This invention relates in general to digital data systems and more particularly to the control of data transfer from a VME bus to a SCSI disk drive.
A need exists to transfer data between a SCSI (Small Computer Systems Interface) device, such as a disk drive, and a VME bus. This requires adapting the SCSI channel, which is a byte-wide data pathway, to the VME bus, which can be either a byte, short word (2 parallel bytes), or long word (4 parallel bytes) pathway. VME bus byte transfers can occur over two sets of data lines, i.e. D0 through D7 or D8 through D15. Short word transfers use data lines D0 through D15. Long word transfers use data lines D0 through D31. Accordingly, the circuit must accommodate each of these pathways, while maintaining the data in the proper sequence regardless of the width of transfer, or of interleaving of the data widths.
The following patents describe several configurations for effecting data transfer which do not satisfy this need due to undue complexity, excessive cost and/or unreliability.
U.S. Pat. No. 4,843,544, issued Jun. 17, 1989, Inventors DuLac et al;
U.S. Pat. No. 4,847,759, issued Jul. 11, 1989, Inventor Oklobdzija.
U.S. Pat. No. 4,805,097, issued Feb. 14, 1989, Inventor DeSanna;
U.S. Pat. No. 4,864,291, issued Sep. 5, 1989, Inventor Korpi;
U.S. Pat. No. 4,783,705, issued Nov. 8, 1988, Inventors Moon et al.;
U.S. Pat. No. 4,716,525, issued Dec. 29, 1987, Inventors Galanyi et al.